Encapsulated droplets and particles are used in a variety of commercial applications, including but not limited to drug delivery, pharmaceuticals, medical procedures, food products, combustion systems, personal care products, and many other industries. Encapsulated droplets and particles typically include a first core material surrounded by a second shell material, wherein the first core material and second shell material are different. Encapsulated droplets and particles may be formed using a variety of different techniques and devices known in the art. Traditional methods and devices for forming encapsulated droplets and particles generally require mechanically combining the core material and shell material in such a way that the shell material surrounds a particle or droplet of the core material.
One conventional method of producing encapsulated droplets and particles relies on dissociation or breakup of a stable capillary microjet, wherein the microjet includes a center column of core material having a sheath of shell material surrounding the core material. By controlling flow parameters and mechanical properties of both core and shell materials, controlled capillary instability of the microjet may be achieved. Such controlled instability leads to breakup of the microjet into a plurality of encapsulated droplets. This technique of encapsulated droplet formation may be referred to as flow focusing encapsulation or stabilized microjet capillary breakup encapsulation. For example, U.S. Pat. No. 6,357,670 to Ganan-Calvo et al. titled “Stabilized Capillary Microjet and Devices and Methods for Producing Same” teaches devices and methods for production of encapsulated droplets by choosing control variables to achieve a desired capillary microjet flow regime allowing controlled breakup of a capillary microjet into spherical droplets of core material surrounded by a layer of shell material. Ganan-Calvo identifies control variables to include flow parameters (pressure, volumetric flow rate), material properties (density, viscosity), and geometric dimensions (orifice diameter). Such control variables may be selected to influence, inter alia, droplet core diameter, shell thickness, outer diameter, and eccentricity between core and shell. Ganan-Calvo further teaches selection of the control variables to influence the stability of the capillary microjet.
Known techniques and devices for producing such particles that rely on selection of control parameters to influence dispersion characteristics may yield inconsistent results. Conventional studies of flow focusing encapsulation generally focus on selection of parameters to produce a stable microjet, and such studies are not aimed at identifying the parameters that lead to undesirable, or bad, results. For example, conventional methods and devices do not intentionally identify relationships between control parameters that lead to non-homogenous concentric droplet breakup or non-monodisperse droplet production.
What is needed, then are improvements in devices and methods for producing encapsulated droplets and particles.